• ZZ (3/3) Feb 13 2006 Why isn't it in D?
• Sean Kelly (8/10) Feb 13 2006 Basically, because Walter isn't entirely happy with any existing
• Walter Bright (3/9) Feb 13 2006 LOL, that's a good summary of the situation.
• Derek Parnell (51/53) Feb 13 2006 Because it means many different things and some are easy to do, some har...
• Chris Miller (5/8) Feb 13 2006 http://www.digitalmars.com/d/attribute.html#const
• nick (2/14) Feb 13 2006 If you have a class A, how do you make a const instance of it?
• Sean Kelly (5/19) Feb 13 2006 I think the closest you could come in D would be to define a custom
• Andrew Fedoniouk (2/7) Feb 13 2006 :-)))
• Chris Miller (7/21) Feb 13 2006 Can only have const reference and assign an instance,
• Andrew Fedoniouk (14/28) Feb 13 2006 class A
• nick (4/42) Feb 13 2006 Can _I_ ask for something more natural? =)
• Derek Parnell (45/60) Feb 13 2006 Thanks Andrew,
• Walter Bright (6/13) Feb 13 2006 With casting and pointers, you'll *always* be able to subvert both the t...
• Derek Parnell (11/27) Feb 13 2006 I guess I didn't make it clear but I think that its a *good* thing that ...
• Walter Bright (4/8) Feb 13 2006 I agree, which fits in with D being a systems level language.
• Dave (22/64) Feb 14 2006 If you add a 'package specifier' to each module declaration then it will...
• Dave (2/6) Feb 14 2006
• Bruno Medeiros (9/25) Feb 14 2006 Not methods, but members. That is: methods and fields, but not inner

ZZ <ZZ zz.com> writes:

Why isn't it in D?
Does any one know why?

Zz

Sean Kelly <sean f4.ca> writes:

ZZ wrote:
 Why isn't it in D?
 Does any one know why?

Basically, because Walter isn't entirely happy with any existing 
implementations (C++ being one such example) and is hoping a better 
solution comes to light.  Feelings on this issue are mixed, because 
while most people seem to agree that the C++ method isn't ideal, many 
still want some checking in place.  This issue competes with the 
bit/bool issue in being the most debated topic on this forum ;-)


Sean

"Walter Bright" <newshound digitalmars.com> writes:

"Sean Kelly" <sean f4.ca> wrote in message 
news:dsr5rm$82h$1 digitaldaemon.com...
 Basically, because Walter isn't entirely happy with any existing 
 implementations (C++ being one such example) and is hoping a better 
 solution comes to light.  Feelings on this issue are mixed, because while 
 most people seem to agree that the C++ method isn't ideal, many still want 
 some checking in place.  This issue competes with the bit/bool issue in 
 being the most debated topic on this forum ;-)

LOL, that's a good summary of the situation. 

Derek Parnell <derek psych.ward> writes:

On Tue, 14 Feb 2006 01:27:29 +0200, ZZ wrote:

 Why isn't it in D?
 Does any one know why?

Because it means many different things and some are easy to do, some hard
and some impossible without hardware/VM support. There is no agreement
about what one means by it.

Walter will address some of the 'const' issues in the (distant?) future but
for now, there is no likelihood of anything like 'const' happening.

For example, why not give us your meaning on const and how you see it
helping your applications. I'm sure we will soon get somebody disagreeing
with some aspects of your ideas :-)

In my case, I do not won't 'const'-qualified data to be actively protected
from change, but I'd like the "-w" switch to tell me about direct attempts
to modify such data, and be quiet about indirect attempts to modify it. A
the data I'm referring to is intrinsic datatypes (int, real, etc...) and
that which is directly (one level deep) owned by the aggregate data
structures (arrays, structs, and objects).

For example:
   class Foo
   {
         char[10] A;
         char[]   B;
         const char[] C;
   }
   const Foo f = new Foo;

   f.A[0] = 'x'; // bad 'cos all of A is owned by f.
   f.B.length = 10; // bad 'cos B is a reference and is owned by f.
   f.B[0] = 'x'; // Okay, 'cos the data B points to is not owned by f.
   f.C.length = 10; // bad 'cos C is a reference and is owned by f.
   f.C[0] = 'x'; // bad, 'cos the data C points to is owned by const C.
   
   // To allow updates to f 
   access (f)
   {
      f.A[0] = 'x'; 
      f.C.length = 10;
      access (f.C)
      {
          f.C[0] = 'x';
      }
   }

This enables the compiler to warn me about accidental updates but still
allows me to make deliberate updates.

But as you can imagine, there are lots of corner cases that need to be
fleshed out and addressed. But the principle is still the same, I want to
be alerted to accidental updates and I want to be able to make deliberate
updates.

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
14/02/2006 10:41:20 AM

"Chris Miller" <chris dprogramming.com> writes:

On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:

 Why isn't it in D?
 Does any one know why?

 Zz

http://www.digitalmars.com/d/attribute.html#const

If you mean "Why isn't D const like c/c++ const?" then searching around  
can find reasons; here's one,  
http://www.digitalmars.com/d/archives/15187.html

nick <nick.atamas gmail.com> writes:

Chris Miller wrote:
 On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:
 
 Why isn't it in D?
 Does any one know why?

 Zz

 
 http://www.digitalmars.com/d/attribute.html#const
 
 If you mean "Why isn't D const like c/c++ const?" then searching around
 can find reasons; here's one,
 http://www.digitalmars.com/d/archives/15187.html

If you have a class A, how do you make a const instance of it?

Sean Kelly <sean f4.ca> writes:

nick wrote:
 Chris Miller wrote:
 On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:

 Why isn't it in D?
 Does any one know why?

 Zz

 http://www.digitalmars.com/d/attribute.html#const

 If you mean "Why isn't D const like c/c++ const?" then searching around
 can find reasons; here's one,
 http://www.digitalmars.com/d/archives/15187.html

 
 If you have a class A, how do you make a const instance of it?

I think the closest you could come in D would be to define a custom 
allocator that places the class instance in the static data area, then 
rely on hardware access protection to flag any attempts at modification.


Sean

"Andrew Fedoniouk" <news terrainformatica.com> writes:

 If you have a class A, how do you make a const instance of it?

 I think the closest you could come in D would be to define a custom 
 allocator that places the class instance in the static data area, then 
 rely on hardware access protection to flag any attempts at modification.

:-)))

can I ask for something more natural, no?

"Chris Miller" <chris dprogramming.com> writes:

On Mon, 13 Feb 2006 21:58:04 -0500, nick <nick.atamas gmail.com> wrote:

 Chris Miller wrote:
 On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:

 Why isn't it in D?
 Does any one know why?

 Zz

 http://www.digitalmars.com/d/attribute.html#const

 If you mean "Why isn't D const like c/c++ const?" then searching around
 can find reasons; here's one,
 http://www.digitalmars.com/d/archives/15187.html

 If you have a class A, how do you make a const instance of it?

Can only have const reference and assign an instance,

const A a;

static this()
{
    a = new A;
}

"Andrew Fedoniouk" <news terrainformatica.com> writes:

"nick" <nick.atamas gmail.com> wrote in message 
news:dsrgvg$hip$1 digitaldaemon.com...
 Chris Miller wrote:
 On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:

 Why isn't it in D?
 Does any one know why?

 Zz

 http://www.digitalmars.com/d/attribute.html#const

 If you mean "Why isn't D const like c/c++ const?" then searching around
 can find reasons; here's one,
 http://www.digitalmars.com/d/archives/15187.html

 If you have a class A, how do you make a const instance of it?


class A
{
    int foo() {  return _foo; }

    package this() {}
    package ~this(){}

// data
    package int _foo;
}

Instances of this class are effectively read-only outside of
your package and are managed by your package.

Or you can consider Ruby way and implement frozen object state.

Andrew.

nick <nick.atamas gmail.com> writes:

Andrew Fedoniouk wrote:
 "nick" <nick.atamas gmail.com> wrote in message 
 news:dsrgvg$hip$1 digitaldaemon.com...
 Chris Miller wrote:
 On Mon, 13 Feb 2006 18:27:29 -0500, ZZ <ZZ zz.com> wrote:

 Why isn't it in D?
 Does any one know why?

 Zz

 http://www.digitalmars.com/d/attribute.html#const

 If you mean "Why isn't D const like c/c++ const?" then searching around
 can find reasons; here's one,
 http://www.digitalmars.com/d/archives/15187.html

 If you have a class A, how do you make a const instance of it?

 
 
 class A
 {
     int foo() {  return _foo; }
 
     package this() {}
     package ~this(){}
 
 // data
     package int _foo;
 }
 
 Instances of this class are effectively read-only outside of
 your package and are managed by your package.
 
 Or you can consider Ruby way and implement frozen object state.
 
 Andrew.
 
 
 
 

Can _I_ ask for something more natural? =)

Seriously, I don't know if const is needed. As far as I can tell, Java
has final and that seems to be enough...

Derek Parnell <derek psych.ward> writes:

On Mon, 13 Feb 2006 19:17:30 -0800, Andrew Fedoniouk wrote:

 If you have a class A, how do you make a const instance of it?

 
 class A
 {
     int foo() {  return _foo; }
 
     package this() {}
     package ~this(){}
 
 // data
     package int _foo;
 }
 
 Instances of this class are effectively read-only outside of
 your package and are managed by your package.

Thanks Andrew,
this is almost there for me too. I did some testing and it works for the
most part. The part I can't seem to get working is that modules in the same
package still can't access the 'package' members.  

Consider my test...

----- m1.d ----
import m2;
void Bar()
{
    Q q;
    q.Foo();
}

---- m2.d ----
import m1;
struct Q
{
 package void Foo() {}
}
-------------

Now I have these in the same directory and compile with "dmd m1 m2 -c" but
get this message "m1.d(5): struct m2.Q member Foo is not accessible". 

However, if I make this change to m2.d ...

---- m2.d ----
import m1;
package struct Q
{
 void Foo() {}
}

------------

now it compiles. But my understanding is that the 'package' modifier only
applies if it is against a method name and not a class declaration.


BTW, the 'package' modifier still let's me do nasty things if I really had
to ...

   Q q;
   real *b;
   *(b = cast(real *)&q) = 3.14;

This compiles even if 'package' or 'private' has been specified, thus
allowing very low-level updating.

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
14/02/2006 3:13:19 PM

"Walter Bright" <newshound digitalmars.com> writes:

"Derek Parnell" <derek psych.ward> wrote in message 
news:oulocmdyp9w8.8tq0o500xmxx$.dlg 40tude.net...
 BTW, the 'package' modifier still let's me do nasty things if I really had
 to ...

   Q q;
   real *b;
   *(b = cast(real *)&q) = 3.14;

 This compiles even if 'package' or 'private' has been specified, thus
 allowing very low-level updating.

With casting and pointers, you'll *always* be able to subvert both the type 
system and any const semantics (unless const data is protected by the 
hardware). The interesting question is whether such deliberate subversion 
invokes defined or undefined behavior. 

Derek Parnell <derek psych.ward> writes:

On Mon, 13 Feb 2006 21:54:37 -0800, Walter Bright wrote:

 "Derek Parnell" <derek psych.ward> wrote in message 
 news:oulocmdyp9w8.8tq0o500xmxx$.dlg 40tude.net...
 BTW, the 'package' modifier still let's me do nasty things if I really had
 to ...

   Q q;
   real *b;
   *(b = cast(real *)&q) = 3.14;

 This compiles even if 'package' or 'private' has been specified, thus
 allowing very low-level updating.

 
 With casting and pointers, you'll *always* be able to subvert both the type 
 system and any const semantics (unless const data is protected by the 
 hardware). The interesting question is whether such deliberate subversion 
 invokes defined or undefined behavior.

I guess I didn't make it clear but I think that its a *good* thing that D
allows this close-to-the-metal coding. There are going to be times when
such anti-social coding is justified.

So is the 'package' issue I also talked about a bug or expected behaviour?

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
14/02/2006 5:49:02 PM

"Walter Bright" <newshound digitalmars.com> writes:

"Derek Parnell" <derek psych.ward> wrote in message 
news:1tpldiq9zop22.1ck8djgnrm2j2$.dlg 40tude.net...
 I guess I didn't make it clear but I think that its a *good* thing that D
 allows this close-to-the-metal coding. There are going to be times when
 such anti-social coding is justified.

I agree, which fits in with D being a systems level language.

 So is the 'package' issue I also talked about a bug or expected behaviour?

I'll have to study it, as it wasn't immediately obvious. 

Dave <Dave_member pathlink.com> writes:

In article <oulocmdyp9w8.8tq0o500xmxx$.dlg 40tude.net>, Derek Parnell says...
this is almost there for me too. I did some testing and it works for the
most part. The part I can't seem to get working is that modules in the same
package still can't access the 'package' members.  

Consider my test...

----- m1.d ----
import m2;
void Bar()
{
    Q q;
    q.Foo();
}

---- m2.d ----
import m1;
struct Q
{
 package void Foo() {}
}
-------------

Now I have these in the same directory and compile with "dmd m1 m2 -c" but
get this message "m1.d(5): struct m2.Q member Foo is not accessible". 

If you add a 'package specifier' to each module declaration then it will work,
which is consistent with the docs:

module test.m1;
import m2;
void Bar()
{
Q q;
q.Foo();
}
;---
module test.m2;
import m1;
struct Q
{
package void Foo() {}
}

However, if I make this change to m2.d ...

---- m2.d ----
import m1;
package struct Q
{
 void Foo() {}
}

------------

now it compiles. But my understanding is that the 'package' modifier only
applies if it is against a method name and not a class declaration.

'package' is ignored here (so is final). I think the only attribute that applies
to an aggregate like that is 'final' for classes. That would explain the issue
below too.

This has caused quite a bit of confusion in the past - I wish the compiler would
flag things like 'private class' because they are ignored and can be misleading.

BTW, the 'package' modifier still let's me do nasty things if I really had
to ...

   Q q;
   real *b;
   *(b = cast(real *)&q) = 3.14;

This compiles even if 'package' or 'private' has been specified, thus
allowing very low-level updating.

Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
14/02/2006 3:13:19 PM

Dave <Dave_member pathlink.com> writes:

In article <dssvnu$1u8a$1 digitaldaemon.com>, Dave says...
'package' is ignored here (so is final). I think the only attribute that applies
to an aggregate like that is 'final' for classes. That would explain the issue

That should read "so is private".

This has caused quite a bit of confusion in the past - I wish the compiler would
flag things like 'private class' because they are ignored and can be misleading.

Bruno Medeiros <daiphoenixNO SPAMlycos.com> writes:

Derek Parnell wrote:
 ------------
 
 now it compiles. But my understanding is that the 'package' modifier only
 applies if it is against a method name and not a class declaration.
 
 
 BTW, the 'package' modifier still let's me do nasty things if I really had
 to ...
 
    Q q;
    real *b;
    *(b = cast(real *)&q) = 3.14;
 
 This compiles even if 'package' or 'private' has been specified, thus
 allowing very low-level updating.
 

Not methods, but members. That is: methods and fields, but not inner 
declarations. I don't find this behavior desirable, I think protection 
attributes should work orthogonally to all entities in declaration 
blocks/scopes.

-- 
Bruno Medeiros - CS/E student
"Certain aspects of D are a pathway to many abilities some consider to 
be... unnatural."